SPECIFICATION OF SYNAPTIC CONNECTIONS BETWEEN SENSORY AND MOTOR NEURONS IN THE DEVELOPING SPINAL-CORD
SPECIFICATION OF SYNAPTIC CONNECTIONS BETWEEN SENSORY AND MOTOR NEURONS IN THE DEVELOPING SPINAL-CORD
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DOI：
10.1002/neu.480210104
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发表时间：
1990-01-01
期刊：
影响因子：
--
通讯作者：
MENDELSON, B
中科院分区：
文献类型：
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作者：
FRANK, E;MENDELSON, B
本文描述了青蛙和小鸡单突触牵张反射中突触连接的规范机制的实验研究。支配牛蛙肱三头肌的感觉神经元是在感觉神经发生的整个过程中产生的，似乎与克隆无关。相反，这些感觉神经元的外周靶点在决定它们与运动神经元的中枢连接中起着重要作用。发育中的胸部感觉神经元投射到前肢的新目标，投射到肱脊髓，而它们通常不会这样做。此外，这些外来的感觉神经元与现在功能上合适的臂运动神经元形成单突触兴奋性连接。神经元活动的正常模式对于特定中枢连接的形成不是必需的。在突触发生期间，用箭毒对发育中的小鸡胚胎进行神经肌肉阻滞，仍然会导致正确的感觉-运动连接的形成。在这个过程中，传入纤维之间的竞争性相互作用似乎也不重要。当投射到前肢的感觉神经元的数量在发育过程中急剧减少时，每个传入神经元仍然与正常神经元一样，进行强度和特异性相同的中枢连接。这些结果进行了讨论，参考视网膜神经节细胞的发展和他们的预测到大脑。虽然这两个系统的许多方面是相似的，但模式化的神经活动似乎在视觉通路的发展中发挥着比这里描述的脊髓反射通路更重要的作用。
Experimental studies of mechanisms underlying the specification of synaptic connections in the monosynaptic stretch reflex of frogs and chicks are described. Sensory neurons innervating the triceps brachii muscles of bullfrogs are born throughout the period of sensory neurogenesis and do not appear to be related clonally. Instead, the peripheral targets of these sensory neurons play a major role in determining their central connections with motoneurons. Developing thoracic sensory neurons made to project to novel targets in the forelimb project into the brachial spinal cord, which they normally never do. Moreover, these foreign sensory neurons make monosynaptic excitatory connections with the now functionally appropriate brachial motoneurons. Normal patterns of neuronal activity are not necessary for the formation of specific central connections. Neuromuscular blockade of developing chick embroys with curare during the period of synaptogenesis still results in the formation of correct sensory‐motor connections. Competitive interactions among the afferent fibers also do not seem to be important in this process. When the number of sensory neurons projecting to the forelimb is drastically reduced during development, each afferent still makes central connections of the same strength and specificity as normal. These results are discussed with reference to the development of retinal ganglion cells and their projections to the brain. Although many aspects of the two systems are similar, patterned neural activity appears to play a much more important role in the development of the visual pathway than in the spinal reflex pathway described here.